Antifuse structures, methods, and applications

ABSTRACT

A typical integrated circuit includes millions of microscopic transistors, resistors, and other components interconnected to define a circuit, for example a memory circuit. Occasionally, one or more of the components are defective and fabricators selectively replace them by activating spare, or redundant, components included within the circuit. One way of activating a redundant component is to rupture an antifuse that effectively connects the redundant component into the circuit. Unfortunately, conventional antifuses have high and/or unstable electrical resistances which compromise circuit performance and discourage their use. Accordingly, the inventors devised an exemplary antifuse structure that includes three normally disconnected conductive elements and a programming mechanism for selectively moving one of the elements to electrically connect the other two. The programming mechanism includes a chemical composition that when heated releases a gas into a chamber to move one element, like a piston, from the bottom of the chamber to contact two elements overhanging the top of the chamber. This embodiment ultimately promises better performance because the element that completes the electrical connection has a relatively low and relatively stable resistance.

TECHNICAL FIELD

The present invention concerns integrated-circuit wiring, particularlyprogrammable electrical connections, such as fuses and antifuses, andmethods of making them.

BACKGROUND OF THE INVENTION

Integrated circuits, the key components in thousands of electronic andcomputer products, are interconnected networks of electrical componentsfabricated on a common foundation, or substrate. Fabricators typicallyuse various techniques, such as layering, doping, masking, and etching,to build thousands and even millions of microscopic resistors,transistors, and other electrical components on a silicon substrate,known as a wafer. The components are then wired, or interconnected,together to define a specific electric circuit, such as a computermemory.

Because of the difficulties of making and interconnecting millions ofmicroscopic components, fabricators expect that one or more parts of anintegrated circuit will fail to operate correctly. However, rather thandiscard the entire integrated circuit because of a few defective parts,fabricators sometimes include extra, or redundant, parts in integratedcircuits to selectively replace defective parts. For example, memoryfabricators sometimes include redundant memory cells to replacedefective memory cells in an integrated memory circuit. Fabricators canthen test the memory circuit for defective cells and activate one ormore of the redundant cells to save the integrated circuit.

Activating a redundant part often entails opening or closing, that is,programming, one or more programmable electrical connections between theredundant part and the rest of the integrated circuit. In general, thereare two types of programmable electrical connections: fuses andantifuses. A fuse is a normally closed electrical connection which canbe opened typically using a laser to melt and vaporize a portion of thefuse. An antifuse, on the other hand, is normally open and requires someaction to close the connection, that is, to electrically connect one endof the antifuse to the other.

Antifuses typically include a thin, insulative layer sandwiched betweentwo conductors. Closing, or programming, an antifuse generally requiresapplying a large voltage across the two conductors. The large voltagecreates an electric field which exceeds the breakdown strength of theinsulative layer, thereby rupturing the insulative layer andelectrically connecting the two conductors.

Unfortunately, antifuses based on the breakdown or rupturing of aninsulative layer perform poorly. Specifically, the resulting electricalconnections often have high electrical resistances which ultimatelywaste power and slow down the transfer of electrical signals throughintegrated circuits. Moreover, these high resistances tend to varysignificantly over time and thus make it difficult for integratedcircuits to perform consistently as they age. Additionally, therupturing process inevitably varies significantly from antifuse toantifuse within the same integrated circuit, introducing undesirabledifferences in the electrical traits of various parts of the circuit andthus compromising circuit performance. These and other performanceconcerns have ultimately led some fabricators to avoid using antifuses.

Accordingly, there is a need for better antifuses and antifuseprogramming techniques.

SUMMARY OF THE INVENTION

To address these and other needs, the inventors devised an integratedantifuse structure that includes two conductive elements and aprogramming mechanism for selectively moving one of the elementsrelative to the other, to, for example, bring them into electricalcontact with each other. More specifically, one embodiment forms achamber in an integrated circuit, with two conductive elementsoverhanging the top of the chamber and a third conductive element lyingon the bottom of the chamber. The bottom of the chamber includes achemical compound that when heated sufficiently rapidly evolves, orreleases, a gas, such as hydrogen, nitrogen, or oxygen. The rapidrelease of gas into the chamber creates a force that moves the thirdelement, like a piston, from the bottom of the chamber to contact thetwo elements overhanging the top of the chamber, thereby completing anelectrical connection. The exemplary embodiment uses copper elements andultimately promises better performance than conventional rupture-basedantifuses because the copper elements have reproducible electricalresistances that remain stable during antifuse programming andsubsequent aging.

Other facets of the invention include methods of making and operatingantifuses and several integrated-circuit applications for antifuses inaccord with the invention. For example, one integrated-circuitapplication is a programmable logic array, and another is an integratedmemory circuit having redundant memory cells. The invention, however,can be applied to any integrated circuit where a programmable electricalconnection, such as a fuse or antifuse, is desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an integrated-circuit assembly 10 atan early fabrication stage, including substrate 12, adhesion layers 14 aand 14 b, and conductors 16 a and 16 b;

FIG. 2 is a cross-sectional view of the FIG. 1 integrated-circuitassembly after formation of an insulative layer 18 having an opening, orchamber, 20 which exposes portions of conductors 16 a and 16 b;

FIG. 3 is a cross-sectional view of the FIG. 2 integrated-circuitassembly, after formation of a metal layer 22, a metal-oxide layer 24,and a conductive layer 26 having parts 26 a and 26 b which overhangchamber 20 and part 26 c which lies within chamber 20 on metal-oxidelayer 24;

FIG. 4 is a cross-sectional view of the FIG. 3 assembly after chargingmetal layer 22 with hydrogen to form a metal-hydride layer 22′;

FIG. 5 is a cross-sectional view of the FIG. 4 assembly after applyingan electrical voltage to conductors 16 a and 16 b that causesmetal-hydride layer 22′ to release hydrogen gas into chamber 20, whichin turn moves conductive element 26 c into contact with conductiveelements 26 a and 26 b;

FIG. 6 is a cross-sectional view of alternative antifuse structure 10′which includes a separate thin-film resistor 21 connected to conductors16 a and 16 b and a gas-releasing layer 25;

FIG. 7 is a partial schematic diagram of an integrated memory circuit 30incorporating at least one redundant memory cell and an antifuseresembling the integrated-circuit assembly of FIG. 4 or FIG. 5; and

FIG. 8 is a partial schematic diagram of a programmable logic array 40incorporating several antifuses resembling the integrated-circuitassemblies shown in FIG. 3, 4, 5, or 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description, which references and incorporatesFIG. 1-8, describes and illustrates one or more specific embodiments (orimplementations) of the invention. These embodiments, offered not tolimit but only to exemplify and teach the invention, are shown anddescribed in sufficient detail to enable those skilled in the art toimplement or practice the invention. Thus, where appropriate to avoidobscuring the invention, the description may omit certain informationknown to those of skill in the art.

FIG. 1-5 show a number of exemplary integrated-circuit assemblies, whichtaken collectively and sequentially, illustrate an exemplary method ofmaking and using an exemplary antifuse (or more broadly a programmableelectrical connection) within the scope of the present invention. Themethod, as shown in the cross-sectional view of FIG. 1, begins withformation of an integrated-circuit assembly or structure 10, which canexist within any integrated circuit, for example, an integrated memorycircuit. Assembly 10 includes a substrate 12. The term “substrate,” asused herein, encompasses a semiconductor wafer as well as structureshaving one or more insulative, semi-insulative, conductive, orsemiconductive layers and materials. Thus, for example, the termembraces silicon-on-insulator, silicon-on-sapphire, and other advancedstructures.

Substrate 12 includes adhesion layers 14 a and 14 b and conductors 16 aand 16 b. Conductors 16 a and 16 b, which serve as respective x- andy-address lines for the completed antifuse, occupy trenches having adepth 16 d and are separated by a distance 16 s. Distance 16 s definesthe effective length and thus the electrical resistance of a resistiveheating element formed in later stages of the method. For precisecontrol of this distance, the exemplary method uses a suitably patternedphotoresistive mask and a reactive ion etching process to form shallowwells with vertical sidewalls within substrate 12. Then after formingadhesion layers 14 a and 14 b in the shallow wells, the exemplary methodoverfills them with conductive metal, ultimately using achemical-mechanical planarization to finish the structure. To ensurepredictable resistances, cracks or fissures within conductors 16 a and16 b should be avoided.

In the exemplary embodiment, adhesion layers 14 a and 14 b, whichpromote adhesion of metal to substrate 12, comprise chromium and havethicknesses in the range of 50 to 100 angstroms. Conductors 16 a and 16b are approximately 100-1000 angstroms thick and comprise copper. (Thethickness of conductors 16 a and 16 b should generally be small toreduce lateral heat transfer away from the resistive element duringprogramming of the antifuse.)

In other embodiments, conductors 16 a and 16 b comprise metals, such asaluminum and its alloys, gold, or silver, and nonmetals, such as heavilydoped polysilicon. Other embodiments form adhesion layers 14 a and 14 bfrom materials such as titanium, tungsten, tantalum, and alloys thereof.Dimensions other than those described here are also within the scope ofthe invention. Thus, the invention is not limited to any particulargenus or species of conductive materials or to any genus or species ofadhesion materials or to any particular dimensions or dimensionalrelationships.

FIG. 2 shows that the exemplary method next entails forming aninsulative layer 18 having an opening, or chamber, 20 exposing portionsof substrate 12 and of conductors 16 a and 16 b. (Chamber 20 can also beviewed as an insulative well.) Insulative layer 18 has a thickness 18 tof about 6000 angstroms in the exemplary embodiment and comprises anynumber of materials, for example, silicon dioxide, fluorinated silicondioxide, silicon nitride, silicon oxynitride, aluminum oxide, or apolymer, such as fluorinated polyimide. Any number of techniques, forexample, physical sputtering, low-pressure-chemical-vapor deposition(LPCVD) or plasma-enhanced-chemical-vapor deposition (PECVD), can beused to form layer 18.

Chamber 20, which has a square cross-section (when viewed from the top),has a width 20 w of about 6000 angstroms. Chamber 20 exposes sections ofconductors 16 a and 16 b, which have a width 20 e of about 1000angstroms, measured from a respective sidewall of chamber 20 and arespective conductor edge. In general, width 20 e is selected to ensureoverlap with a resistive element, namely layer 22, formed in subsequentstages of the method. Though not shown in the figure, the exemplarymethod applies and patterns a photoresistive layer to define theperiphery of chamber 20, uses reactive-ion etching to form the chamber,and then removes the photoresistive layer in situ with an oxygen plasma.However, the invention is not limited to any particular method offorming chamber 20 or to any particular chamber dimensions or shapes.Indeed, other embodiments form chambers having smaller or largercross-sectional areas and having round, elliptical, and other arbitraryregular or irregular shapes.

FIG. 3 shows that after forming insulative layer 18, the exemplarymethod sequentially forms a metal layer 22, a metal-oxide layer 24, anda conductive layer 26 having conductive elements 26 a, 26 b, and 26 c.Elements 26 a and 26 b overhang opposing sides of chamber 20, andconductive element 26 c lies within chamber 20 atop metal-oxide layer24.

More particularly, to form metal layer 22, the exemplary method depositsand patterns a photoresist layer and etches layer 18 to expose portionsof conductors 16 a and 16 b and the portion of substrate 12 betweenthem. The method then cleans the exposed conductor and substratesurfaces using a sputtering treatment in an inert gas plasma The inertgas plasma is sufficient to clean these surfaces, but does notsignificantly alter the patterned resist layer. After this cleaning, theexemplary method sputter deposits a 1000-angstrom-thick layer of metalon the floor of chamber 20.

The exemplary embodiment forms metal layer 22 from titanium; however,other embodiments use hafnium, niobium, tantalum, thorium, vanadium,zirconium, and any other metals and alloys having large capacities ofholding hydrogen in solid solution and/or hydride and pseudo-hydridephases. For example, other metals that can hold several hundreds to manythousands of cubic centimeters of hydrogen per 100 grams of metal arelikely to be suitable. More generally, the inventors believe thatvirtually any metal or compound that can hold a gas in the form of asolid solution, hydride, oxide, or nitride, for example, can be adaptedto suit the function of the invention. Thus, the invention is notlimited to the particular metals or gases disclosed here.

Forming metal-oxide layer 24, in the exemplary embodiment, entailsoxidizing metal layer 24 in an oxygen ambient at 50-100° C. for about anhour to provide a thickness of 100-200 angstroms. (This procedure isgenerally suitable for most if not all metals with largehydrogen-holding capacities.) However, other embodiments directlydeposit an insulative metallic oxide on layer 22 rather than using theexemplary oxidation procedure. Additionally, other embodiments usethicker or thinner metal-oxide layers to ensure electrical isolation ofmetal layer 22 from conductive element 26 during subsequent programmingvia conductors 16 a and 16 b. Layer 24 also serves to prevent or reduceadhesion of layer 22 and element 26. Adhesion can also be furtherreduced or mitigated by forming a very thin (about 10-50 angstroms)chemically inert carbon layer (not shown) between layer 22 and element26 c.

In the exemplary embodiment, forming conductive layer 26 entailssequentially sputtering an adhesion-promoting material, such aschromium, and a conductive material, such as copper, onto metal-oxidelayer 24 and the shoulders of chamber 20. The exemplary methods depositsthe adhesion-promoting material to a thickness of 50-to-100 angstromsand the conductive materials to a thickness of about 2000 angstroms. Thetotal thickness of the adhesion-promoting and conductive materials iskept small to prevent the formation of conductive bridges betweenelement 26 c and elements 26 a and 26 b.

In general, conductive layer 26 comprises any material having asignificantly lesser hydrogen solubility than that of metal layer 22,for example, several orders of magnitude less hydrogen solubility.Examples of metals that have relatively small hydrogen solubilities(that is, solubilities on the order of 0.1-to-5 cubic centimeters ofhydrogen per 100 grams of metal) include copper, nickel, silver,molybdenum, aluminum, iron, tungsten, gold, platinum, ruthenium,rhodium, and their alloys. However, with appropriate sizing of chamber20, layer 22, and element 26 c, one may be able to form the antifuseusing lesser differences in hydrogen solubilities.

To complete formation of the antifuse structure after depositingconductive layer 26, the exemplary method patterns it to defineoverhangs, using, for example, ion milling with a resist mask in placeto protect element 26 c within chamber 20. If the portions of conductiveelements 26 a and 26 b overhanging chamber 20 are too short to stopmovement of element 26 c during programming of the antifuse, one canlengthen them in various ways including the following two. First, onecan electro-deposit, or electroplate, additional metal onto theseconductive elements. Plating 500 angstroms of additional metal, forexample, yields overhangs of almost 500 angstroms. This entails usingelements 26 a and 26 b as cathodes during plating and leaving element 26c, within the chamber, unbiased to prevent its plating. This biasarrangement focuses deposition on the top surfaces of elements 26 a and26 b. Second, one can use a directional S-gun to deposit 500 angstromsof metal at a glancing angle on the top surface of layer 26. Forexample, one embodiment of the invention uses a glancing angle of 5 to 9degrees relative the horizontal plane of the substrate. For thisexemplary geometry, these small angles along with a modestly collimatedbeam of metal atoms from a deposition source will preclude formation ofmetal bridges between element 26 c and elements 26 a and 26 b.

FIG. 4 shows that the exemplary method next partially or fully saturatesmetal layer 22 with hydrogen to form a metal-hydride layer 22′. (Theeffect of charging is denoted by the change from the parallelcross-hatching of layer 22 in FIG. 3 to the small circles in FIG. 4.)When titanium is used to form metal layer 22, the fully saturated layer22′ has the composition TiH₂. However, the exemplary embodiment does notrequire full conversion of metal layer 22 to a metal hydride, but onlythe storage of sufficient hydrogen to move element 26 c into contactwith elements 26 a and 26 b. (As used herein, metal hydride encompassesany compound including a metal and hydrogen, such as TiH₂ or a solidsolution of hydrogen in titanium, that is, H—Ti.) Other embodiments canstore lesser amounts of hydrogen to only move element 26 c towardelements 26 a and 26 b should this be desirable to, for example, fostercapacitive coupling of the elements.

To charge or saturate layer 22, the exemplary method heats the antifusestructure of FIG. 3 and introduces hydrogen under pressure. Morespecifically, it heats the antifuse structure to a temperature of400-500° C. and introduces hydrogen under pressures of 0.1 to 1.0atmospheres. Under these condition and without the presence ofconductive element 26 c, metal layer 22 completely converts to metalhydride with a few tens of seconds to a couple of minutes, depending onthe specific hydriding temperature. (This would entail charging thelayer before formation of conductive layer 26.) However, with thepresence of conductive element 26 c, extra time or hydrogen pressure arenecessary to charge layer 22, because of the diffusion rate of hydrogenthrough element 26 c to layer 22.

Experimental values of diffusivity of hydrogen through copper,particularly relevant to the exemplary chromium-copper form ofconductive element 26 c, are somewhat scattered. The range ofdiffusivity values suggest that a hydrogen pressure of one atmosphere issufficient to diffuse hydrogen through a 10,000-angstrom-thick copperplate at 400° C. in quantities sufficient to form TiH₂ at rates rangingfrom 20 to 340 angstroms per minute. These estimates assume that metallayer 22 consists of titanium and that the hydriding process is 100percent efficient. (Hydrogen absorption by metal layer 22 is extremelyfast, compared to hydrogen diffusion through copper.)

Further assuming a titanium hydride formation of 20 angstroms perminutes, for example, suggests that charging for about 50 minutes underthese temperature and pressure conditions would completely convert a1000-angstrom-thick titanium layer 22 into TiH₂. Moreover, increasingthe hydrogen pressure (and thus the hydrogen transport) by a factor often would reduce the charge time by a factor of ten, that is, from about50 minutes to about 5 minutes. Alternatively, one could maintain thehydrogen pressure at 1.0 atmosphere and raise the temperature from 400to 500° C. to reduce the charging time five-fold, that is, from about 50minutes to about 10 minutes. These examples show that very acceptablecombinations of charging temperature and pressure can be employed totransport hydrogen through conductive element 26 c to convert metallayer 22 to metal-hydride layer 22′ in an hour or less.

After saturating or charging layer 22 with hydrogen, the exemplarymethod cools the antifuse structure a few hundred degrees while stillunder the charging pressure to prevent undesirable evolution of hydrogenfrom the layer. At temperatures of about 150° C. and below, the metalhydride is stable.

FIG. 5 shows the results of programming the antifuse of FIG. 4.Programming entails applying a voltage differential in the form of pulseacross conductors 16 a and 16 b. In turn, this causes metal-hydridelayer 22′ to release or evolve hydrogen gas into chamber 20, through aprocess of chemical decomposition. (In embodiments that omit conductors16 a and 16 b, one can apply heat to metal-hydride layer 22′ using alaser, for example.) The release of gas into chamber 20, if achievedrapidly enough, moves conductive element 26 c, like a piston, upwardthrough chamber 20 into contact with conductive elements 26 a and 26 b.If the rate of movement is sufficient, the impact of conductive element26 c with the overhanging portions of elements 26 a and 26 b fuseselement 26 c to elements 26 a and 26 b, thereby forming an electricalconnection.

For illustration, the inventors estimate that a4000-angstrom-by4000-angstrom-by-1000-angstrom (length×width×height)fully saturated titanium-hydride layer 22 can release 3.0×10⁻⁷cubic-centimeters of hydrogen (as measured at one atmosphere and 0° C.)Within the volume of chamber 20, this translates into a pressureexceeding 30,000 atmospheres. Such pressure can accelerate element 26 cto a rate sufficient to fuse the element with elements 26 a and 26 b onimpact. The impact will likely cause some deformation of all threeconductive elements and thus allow much, if not all, of the releasedhydrogen to escape chamber 20.

In the exemplary embodiment, one controls the programming processthrough use of varying programmable voltage pulses which controllablyraise the temperature of the metal-hydride layer to the desired hydrogenevolution temperatures in a time on the order of several microseconds.In the case of TiH₂, hydrogen evolution rates are exceedingly rapid fortemperatures over 400° C., and the hydrogen evolution rates increaserapidly with increasing temperatures above 500-600° C. Assuming thattitanium metal and titanium hydride have approximately the sameelectrical resistivity, namely about 80 micro-ohm-centimeters, suggestsvoltage pulses of 1.25 to 5.0 volts in magnitude and a few microsecondsin duration heat a TiH2 resistive film to temperatures in the 400-800°C. range and thereby release a large fraction of its hydrogen content.

One can also apply lower voltages to “disarm” charged and unprogrammedantifuses selectively through a slower release of gas from metal-hydridelayer 22. Similarly, one can also heat an entire integrated circuitslowly over time to slowly decompose the metal-hydride layer. In thesecases, the hydrogen gas seeps out of chamber 20 without moving element26 c at all or without moving it far enough to form an electricalconnection between elements 26 a and 26 b.

Other possibilities for controlling hydrogen evolution temperatures frommetal-hydride layer 22 stem from understanding that metal hydrides havea wide range of absorption-desorption properties. For example, vanadiumhydride (VH_(x) where x is about one) contains only half as muchhydrogen as TiH₂ but evolves almost all its hydrogen at temperature of200 to 300° C. Additionally, one can form alloy compositions ofhigh-hydrogen-solubility metals to obtain metal hydride layers withtailored hydrogen absorption-desorption characteristics. For example, aV-Ti alloy film charged with hydrogen evolves its hydrogen at atemperature intermittent between that characteristic of VH_(x) and TiH₂.

Materials for Other Embodiments of the Antifuse Structure

As noted earlier, metal layer 22 can be formed from a wide range ofmetals that can hold or store hydrogen in sufficient evolvablequantities to serve the purpose of the invention. Additionally, thereare a number of other compounds, including oxides, carbonates, andnitrides, that have capacity for storing or holding nitrogen or oxygenin generous amounts. Examples of these compounds include: Pb₃O₄ (550),PbO₂ (315), HgO (430), Ag₂O (185), MnO₂ (480), Ag₂O (185), K₃N (355),Rb₃N (415), ReN_(0.43) (280), Co₃N (380), Ni₃N (420), and Cd₃N₂ (320).The parenthetical temperatures are the temperatures (in degrees Celsius)at which each compound dissociates and evolves oxygen or nitrogen gas.For example, Pb₃O₄ evolves oxygen gas at 550° C., and K₃N evolvesnitrogen at 355° C. However, unlike metal hydrides, these compoundsgenerally do not function well as thin-film resistors and require aseparate heating source or element to trigger evolution of oxygen ornitrogen.

Accordingly, FIG. 6 shows an exemplary embodiment of an antifusestructure 10′ which applies one or more of these compounds in a manneranalogous to the metal hydrides in FIGS. 3 and 4. In particular,antifuse structure 10′ is identical to the structure in FIGS. 3 and 4,except for a separate thin-film resistive element 21 and a gas-releasinglayer 25, which replace layers 22 and 24. (For electrical isolation, onecan also include an insulative layer between layers 21 and 25.) Asexplained above, one of ordinary skill can form layer 25 from a widerange of oxides, carbonates, and nitrides, indeed virtually any compoundthat releases a gas. Moreover, if desirable, one could form layer 25from a “gas chargeable” precursor compound and then charge it, as, forexample, metal layer 22 was charged with hydrogen, to form agas-releasing compound.

Examples of materials suitable for resistive element 22 includetantalum-aluminum alloy (Ta—Al), nichromium (Ni—Cr), and hafniumdiboride (HfB₂). These and other materials generate high temperatures inshort time periods under appropriate electrical stimulus. Thus, as inantifuse structure 10, programming antifuse structure 10′ entailsapplying a suitable voltage pulse to conductors 16 a and 16 b, which inturn causes resistive element 21 to generate sufficient heat to evolvegas from gas-releasing layer 25 and to thereby move conductive element26 c into contact with conductive elements 26 a and 26 b (as shown inFIG. 5.)

Exemplary Integrated-Circuit Applications of the Antifuse Structure

The antifuse of the present invention, particularly the exemplaryantifuse structures of FIG. 3 (disarmed or uncharged), FIGS. 4 and 6(unprogrammed), and FIG. 5 (programmed) are suitable for virtually anyintegrated circuit where a fuse or antifuse is desirable. Two exemplaryintegrated circuit applications are shown in FIGS. 7 and 8.

FIG. 7 is a partial schematic diagram of a generic integrated memoryaddress circuit 30 incorporating several antifuses 35 a-35 d in accordwith the present invention. In many embodiments, the integrated circuitis part of a larger system, such as computer system or more generally acomputerized system including a microprocessor or digital signalprocessor coupled to the memory circuit. In addition to the antifuses,memory circuit 30 includes a set of address transistors 32 a-32 h, a setof redundant address transistors 34 a-34 d, and conventional laser fuses36 a-36 d. Address transistors 32 a-32 h are conventionally used toaddress rows 38 a-38 d in the memory array. Each row includes one ormore memory cells. (For clarity, the figure omits many conventionalfeatures of integrated memory circuits.) One or more of antifuses 35a-35 d and one or more of laser fuses 36 a-36 d can be selectivelyprogrammed to replace one or more of memory rows 38 a-38 d withredundant memory row 34. In some embodiments, one or more of theantifuses are programmed and one or more others remain unprogrammed, andin some embodiments all the antifuses are either programmed orunprogrammed.

FIG. 8 shows a partial schematic diagram of a programmable logic array40 incorporating several antifuses 46 a-46 g in accord with theintegrated-circuit assemblies shown in FIG. 3, 4, 5, or 6. Morespecifically, logic array 40, patterned after a NOR-NORfield-programmable array (FPLA), includes NOR sub-arrays 40 a and 40 b,representative inputs 42 a and 42 b, field-effect transistors 44 a-44 h,antifuses 46 a-46 g, and representative outputs 48 a and 48 b. With theexception for the novel antifuses and related programming techniques,array 40 operates in accord with conventional programmable logic arrays.Although shown with field-effect transistors, the array can beimplemented using other transistor technologies, such as bipolarjunctions transistors or mixed transistors technologies, such asbipolars and field-effect transistors. In some embodiments, logic array40 is coupled to a microprocessor or digital signal processor in alarger system.

CONCLUSION

In furtherance of the art, the inventor has devised an antifusestructure, a method of making the antifuse structure, and relatedmethods of programming, using, and arming and disarming antifuses. Theexemplary embodiment of the antifuse structure includes three normallydisconnected (or connected) conductive elements and a programmingmechanism for selectively moving one of the elements to electricallyconnect (or disconnect) the other two, or more broadly, moving oneelement relative another element.

The exemplary programming mechanism includes a chemical composition thatwhen exposed to sufficient heat rapidly releases a gas that moves aconductive element, like a piston, into contact with two other elementsThis embodiment ultimately promises better performance than conventionalrupture-based antifuses because the conductive element that completesthe electrical connection has a resistance that is relatively unaffectedby the programming process and that remains relatively constant as itages.

The embodiments described above are intended only to illustrate andteach one or more ways of practicing or implementing the presentinvention, not to restrict its breadth or scope. The actual scope of theinvention, which encompasses all ways of practicing or implementing theconcepts of the invention, is defined only by the following claims andtheir equivalents.

1. A method of making an antifuse in an integrated-circuit assembly, themethod comprising: forming an opening in an insulative layer; forming ametal layer in the opening; forming a metal-oxide layer on the metallayer, forming a conductive layer on the metal-oxide layer; and formingat least one conductive member on the insulative layer and overhangingthe opening.
 2. The method of claim 1, wherein the metal layer in theopening comprises at least one of titanium, hafnium, niobium, tantalum,thorium, vanadium, and zirconium.
 3. The method of claim 1, wherein theconductive layer comprises at least one of aluminum, gold, silver, andcopper.
 4. The method of claim 1, wherein the conductive member on theinsulative layer overhangs the opening by at least 250 angstroms.
 5. Amethod of making an antifuse in an integrated-circuit assembly, themethod comprising: forming an opening in an insulative layer, with theopening exposing one or more conductors; forming a metal layer in theopening; forming a metal-oxide layer on the metal layer and within theopening; forming a conductive layer on the metal-oxide layer and withinthe opening; and forming at least one conductive member on theinsulative layer and overhanging the opening.
 6. The method of claim 5,wherein the metal layer in the opening comprises at least one oftitanium, hafnium, niobium, tantalum, thorium, vanadium, and zirconium.7. The method of claim 5, wherein the conductive layer comprises atleast one of aluminum, gold, silver, and copper.
 8. The method of claim5, wherein the conductive member on the insulative layer overhangs theopening by at least 250 angstroms.
 9. A method of making an antifuse inan integrated-circuit assembly, the method comprising: forming anopening in an insulative layer; forming a metal layer in the opening;forming a metal-oxide layer on the metal layer; forming a conductivelayer on the metal-oxide layer; forming at least one conductive memberon the insulative layer and overhanging the opening; and at leastpartially saturating the metal layer with a gas.
 10. The method of claim9, wherein the metal layer in the opening comprises at least one oftitanium, hafnium, niobium, tantalum, thorium, vanadium, and zirconium.11. The method of claim 9, wherein the conductive layer comprises atleast one of aluminum, gold, silver, and copper.
 12. The method of claim9, wherein the conductive member on the insulative layer overhangs theopening by at least 250 angstroms.
 13. A method of making an antifuse inan integrated-circuit assembly, the method comprising: forming anopening in an insulative layer, with the opening exposing at least oneconductor; forming a metal layer in the opening; forming a metal-oxidelayer on the metal layer and within the opening, forming a conductivelayer on the metal-oxide layer and within the opening; forming at leastone conductive member on the insulative layer and overhanging theopening; and at least partially saturating the metal layer with a gascomprising more than trace quantities of hydrogen or nitrogen.
 14. Amethod of making an antifuse in an integrated-circuit assembly, themethod comprising: forming an opening in an insulative layer, with theopening exposing at least one conductor; forming a metal layer in theopening; forming a metal-oxide layer on the metal layer and within theopening, forming a conductive layer on the metal-oxide layer and withinthe opening; forming at least one conductive member on the insulativelayer and overhanging the opening; and saturating the metal layer with agas comprises converting at least a portion of the metal layer into ametal hydride.
 15. A method of making an antifuse in anintegrated-circuit assembly, the method comprising: forming an openingin an insulative layer, with the opening exposing one or moreconductors; forming a metal layer in the opening, the metal layerconsisting essentially of titanium, hafrium, niobium, tantalum, thorium,vanadium, or zirconium; forming a metal-oxide layer on the metal layerand within the opening; forming a conductive layer on the metal-oxidelayer and within the opening; and forming at least one conductive memberon the insulative layer and overhanging the opening.
 16. The method ofclaim 15, wherein the conductive member on the insulative layeroverhangs the opening by at least 250 angstroms.
 17. A method of makingan antifuse in an integrated-circuit assembly, the method comprising:forming an opening in an insulative layer, with the opening exposing oneor more conductors; forming a metal layer in the opening, the metallayer consisting essentially of titanium; forming a metal-oxide layer onthe metal layer and within the opening; forming a conductive layer onthe metal-oxide layer and within the opening; and forming at least oneconductive member on the insulative layer and overhanging the opening.18. The method of claim 17, wherein the conductive member on theinsulative layer overhangs the opening by at least 250 angstroms.
 19. Amethod of making an antifuse in an integrated-circuit assembly, themethod comprising: forming an opening in an insulative layer, with theopening exposing one or more conductors; forming a metal layer in theopening, the metal layer consisting essentially of hafnium; forming ametal-oxide layer on the metal layer and within the opening; forming aconductive layer on the metal-oxide layer and within the opening; andforming at least one conductive member on the insulative layer andoverhanging the opening.
 20. The method of claim 19, wherein theconductive member on the insulative layer overhangs the opening by atleast 250 angstroms.
 21. A method of making an antifuse in anintegrated-circuit assembly, the method comprising: forming an openingin an insulative layer, with the opening exposing one or moreconductors; forming a metal layer in the opening, the metal layerconsisting essentially of niobium; forming a metal-oxide layer on themetal layer and within the opening; forming a conductive layer on themetal-oxide layer and within the opening; and forming at least oneconductive member on the insulative layer and overhanging the opening.22. The method of claim 21, wherein the conductive member on theinsulative layer overhangs the opening by at least 250 angstroms.
 23. Amethod of making an antifuse in an integrated-circuit assembly, themethod comprising: forming an opening in an insulative layer, with theopening exposing one or more conductors; forming a metal layer in theopening, the metal layer consisting essentially of thorium; forming ametal-oxide layer on the metal layer and within the opening; forming aconductive layer on the metal-oxide layer and within the opening; andforming at least one conductive member on the insulative layer andoverhanging the opening.
 24. The method of claim 23, wherein theconductive member on the insulative layer overhangs the opening by atleast 250 angstroms.
 25. A method of making an antifuse in anintegrated-circuit assembly, the method comprising: forming an openingin an insulative layer, with the opening exposing one or moreconductors; forming a metal layer in the opening, the metal layerconsisting essentially of vanadium; forming a metal-oxide layer on themetal layer and within the opening, forming a conductive layer on themetal-oxide layer and within the opening; and forming at least oneconductive member on the insulative layer and overhanging the opening.26. The method of claim 25, wherein the conductive member on theinsulative layer overhangs the opening by at least 250 angstroms.
 27. Amethod of making an antifuse in an integrated-circuit assembly, themethod comprising: forming an opening in an insulative layer, with theopening exposing one or more conductors; forming a metal layer in theopening, the metal layer consisting essentially of tantalum; forming ametal-oxide layer on the metal layer and within the opening; forming aconductive layer on the metal-oxide layer and within the opening; andforming at least one conductive member on the insulative layer andoverhanging the opening.
 28. The method of claim 27, wherein theconductive member on the insulative layer overhangs the opening by atleast 250 angstroms.
 29. A method of making an antifuse in anintegrated-circuit assembly, the method comprising: forming an openingin an insulative layer, with the opening exposing one or moreconductors; forming a metal layer in the opening, the metal layerconsisting essentially of zirconium; forming a metal-oxide layer on themetal layer and within the opening; forming a conductive layer on themetal-oxide layer and within the opening; and forming at least oneconductive member on the insulative layer and overhanging the opening.30. The method of claim 29, wherein the conductive member on theinsulative layer overhangs the opening by at least 250 angstroms.
 31. Amethod of making an antifuse in an integrated-circuit assembly, themethod comprising: forming an opening in an insulative layer, with theopening exposing one or more conductors; forming a metal layer in theopening, the metal layer consisting essentially of titanium, hafnium,niobium, or tantalum; forming a metal-oxide layer on the metal layer andwithin the opening; forming a conductive layer on the metal-oxide layerand within the opening; and forming at least one conductive member onthe insulative layer and overhanging the opening.
 32. The method ofclaim 31, wherein the conductive member on the insulative layeroverhangs the opening by at least 250 angstroms.
 33. A method of makingan antifuse in an integrated-circuit assembly, the method comprising:forming an opening in an insulative layer, with the opening exposing oneor more conductors; forming a metal layer in the opening, the metallayer consisting essentially of thorium, vanadium, or zirconium; forminga metal-oxide layer on the metal layer and within the opening; forming aconductive layer on the metal-oxide layer and within the opening; andforming at least one conductive member on the insulative layer andoverhanging the opening.
 34. The method of claim 33, wherein theconductive member on the insulative layer overhangs the opening by atleast 250 angstroms.
 35. A method of making an antifuse in anintegrated-circuit assembly, the method comprising: forming an openingin an insulative layer, with the opening exposing one or moreconductors; forming a metal layer in the opening, the metal layerconsisting essentially of titanium, hafnium, niobium, tantalum, thorium,vanadium, or zirconium; forming a metal-oxide layer on the metal layerand within the opening; forming a conductive layer on the metal-oxidelayer and within the opening, the conductive layer comprising more thantrace quantities of aluminum, gold, silver, and/or copper; and formingat least one conductive member on the insulative layer and overhangingthe opening.
 36. The method of claim 35, wherein the conductive memberon the insulative layer overhangs the opening by at least 250 angstroms.37. An method of making an antifuse structure in an integrated circuitassembly, comprising: forming a chamber having a bottom and a top andone or more insulative interior walls extending between the top andbottom; forming a conductive layer within the chamber; forming a layerwithin the chamber between the conductive layer and the bottom of thechamber, and comprising a material having a hydrogen-gas-solubility atleast 10 times greater than that of at least a portion of the conductivelayer; and forming first and second conductive members overhanging thetop of the chamber.
 38. The method of claim 37 wherein the forming theinsulative chamber comprises: forming an insulative layer on thesubstrate; and forming an opening exposing a portion of the substrate,with the exposed portion of the substrate defining at least a portion ofthe bottom of the chamber and the opening defining the interiorsidewalls of the chamber.
 39. The method of claim 37 wherein the firstand second conductive members overhang the chamber by at least 250angstroms.
 40. The method of claim 37, wherein the layer comprises atleast one of titanium, hafnium, niobium, tantalum, thorium, vanadium,and zirconium, and hydrogen in solid solution or hydride phases.
 41. Themethod of claim 37, wherein the layer within the chamber comprises Pb₃O₄, PbO₂, HgO, Ag₂O, MnO₂, Ag₂O, K₃N, Rb₃N, ReN_(0.43), Co₃N, Ni₃ N, orCd₃N₂.
 42. The method of claim 37, wherein the conductive layercomprises at least one of aluminum, copper, silver, and gold.